Extensional Relaxation Time, Pinch-Off Dynamics, and Printability of Semidilute Polyelectrolyte Solutions

Quantitative studies of capillary-driven thinning and pinch-off dynamics of semidilute polyelectrolyte solutions, and their response to extensional flows, typically encountered in drop formation applications, are relatively rare and are the focus of this contribution. Here the pinch-off dynamics and extensional rheology of two model polyelectrolytes-poly(sodium 4-styrenesulfonate) (NaPSS) and poly(acrylic acid) (PAA)-in two different solvents are characterized by using Dripping-onto-Substrate (DoS) rheometry. Unlike shear relaxation time that decreases with increase in concentration in the unentangled, semidilute solutions, the extensional relaxation time of PAA solutions increases with an exponent of 1/2, and the entangled semidilute solutions also exhibit a stronger concentration dependence of 3/2. In contrast, the extensional relaxation time is not measurable for the unentangled, semidilute aqueous NaPSS solutions, though entangled NaPSS solutions show concentration-dependent values. The experiments and analysis described herein elucidate how the interplay of stretching due to electrostatics and hydrodynamics influences extensional rheology response and printability of polyelectrolyte dispersions.